classes referring to themselves

[davikokar]

Hallo,
let's say that I have a class Person that has some attributes like name, partner (another Person), mother (another Person), etc. The class refers to itself and I would write something like this:

abstract class Person
{
    public String name = "<unknown>";
    private Person father;
    private Person mother;
    private Person partner;
    public Person(String s1) {name = s1;}
}

now I would like to create a method that makes two persons refer to each other, like marriedTo(Person):

I wrote this code:

	public void marriedTo (Person p1)
	{
		try
		{
			if (this.partner != null || p1.partner != null)
			{
				throw new BigamyException();
			}
			else
			{
				this.partner.name = p1.name;
				p1.partner.name = this.name;
			}
		}
		catch (BigamyException e)
		{
			System.out.println("Illegal marriage");
		}
	}

If I instanciate two persons and make them married I get an a NullPointerException. I don't understand why. Does someone has an hint? thanks

 

[tom62]

Your else statement is executed when this.partner or p1.partner == null. This means that "this.partner.name = p1.name" or "p1.partner.name = this.name" always causes a NullPointerException.

 

[Diancecht]

I really love the "BigamyException"

Did you consider writing a setParner method?



Cheers,
Dian

 

[Canelas]

Hi!
Check to see of p1 is null. I don't think you're checking that.
On the other hand, i think you'll have to instanciate the person objects.
And diancecht is right. You should use get and set methods.

On wich object does he get the exception?